We have in the past concentrated our scientific efforts on two fronts, namely 1) the development of new and improved neuroanatomical techniques, and 2) the application of these techniques to the study of primary and higher order olfactory connexions. The current grant period has to a certain extent been a transition period, not only in the senses that we have moved our laboratory from MIT to the University of Virginia, but also because the methodology previously employed in this research has been supplemented, and partly replaced, by more sensitive experimental methods, some of which have been developed in our laboratory. In this application, continued research support is requested for experimental neuroanatomical investigations aimed at improving our knowledge of the organization of the basal forebrain in mammals. To accomplish this we intend to study three mutually interrelated subjects: 1) the internal organization of the afferent and efferent connexions of the olfactory cortex; 2) the pathways by which the olfactory bulb is related to the rest of the forebrain in general, and to diencephalon in particular, and 3) the ventral strio-pallidal system. The experimental analysis will be aided by a combination of various light- and electron microscopic tracing techniques, including degeneration methods, the autoradiographic technique and different horseradish peroxidase methods.